The drama opens on the battlefield before the gates of Troy, where the Greeks are besieging the city and are interrupted by belligerent Amazons who attack and endanger the Greek princes. The Greeks, distracted from capturing Troy as their leader Agamemnon has ordered, try to contact the Amazon queen Penthesilea to understand her motives.

In the second scene the Greeks learn that Penthesilea has captured their hero Achilles. The messenger provides a vivid account of the Amazons' surprise attack. They surrounded Achilles, who first freed himself and tried to flee until his horses and his cart collapsed. Penthesilea and her followers drew closer, but when the queen toppled and fell, he had another chance to flee, and escaped.

In the fourth scene the Greeks welcome Achilles and acclaim him for his escape. Meanwhile, the Amazons rashly celebrate their victory, whereupon Penthesilea gets furious. Her fury culminates in a quarrel with Prothoe, her most intimate confidante and soulmate. The reason is that Prothoe, as the queen later learns, has fallen in love with one of the Greek prisoners of war. At the end of the scene they settle their dispute, because Penthesilea cannot live without the devoted Prothoe.

Now, the Archpriestess gets onto the scene, with her maidens, who are plucking roses for their queen's first victory. Competing for the most and prettiest roses, the girls start to quarrel. Their dispute is interrupted by an Amazon in gear who announces that the Greek prisoners won't accept any hospitality.

The following scene shows an Amazon captain report to the Archpriestess about the fighting between Penthesilea and Achilles. Prothoe tries to convince her leader to return home, but the queen refuses to listen and insists on staying at the place.

This proves to be fatal, because the Greeks start their attack very soon after. Penthesilea refuses to flee, not even on the counseling of her closest confidants and the priestesses with Prothoe declaring to be willing to stay with her and meet their fate.

The central dynamic of the play lies in the mutual passion of Achilles and Penthesilea. Kleist reverses the narrative found in Homer: Achilles does not kill, but rather is killed – due to a characteristically Kleistian misunderstanding of his intentions – by the Amazonian queen. When Penthesilea recognizes her mistake, she causes her own death, through force of internal self-directed will.